The invention relates, in general, to semiconductor devices and, more particularly, to an exposure mask and a method of forming a contact hole of a semiconductor device using the same, in which micro patterns can be formed.
In processes for manufacturing semiconductor devices, a variety of patterns for forming a bit line contact holes, drain contact holes, and so forth are formed by photolithography processes. In such a photolithography process, a photoresist pattern is formed on a wafer by coating a photoresist layer and exposing and developing the photoresist layer employing an exposure mask reticle. Desired patterns are formed by an etch process using the photoresist pattern as a mask. The exposure mask is fabricated by forming a nontransparent chrome pattern on a transparent substrate, such as a quartz substrate. In order to form contact holes having a cross section of the same size and shape, transparent patterns that are opened only in the nontransparent chrome pattern must have the same size and shape.
However, the photoresist pattern formed on the wafer through the photolithography process is greatly distorted compared with a pattern formed in the exposure mask. Distortion is generated by an optical proximity effect in which light passing through the exposure mask pattern generates interference between neighboring patterns in the photolithography process. The optical proximity effect becomes profound when the size of a pattern to be resolved is smaller than that of the wavelength of a light source. Accordingly, there is a problem when the critical dimension of the contact hole pattern formed in the semiconductor substrate is smaller than that of a desired pattern.
FIG. 1 is a scanning electron microscope (SEM) photograph of photoresist patterns of 60 nm in size, which are formed by using an exposure mask having transparent patterns with the same shape and size.
As shown in FIG. 1, even though photoresist patterns having the transparent patterns with the same shape and size have been used, they are distorted and very irregular. The irregular photoresist patterns are further distorted as the size decreases. This problem must be solved in order to fabricate high-integrated semiconductor devices.